1. Field of the Invention
Embodiments disclosed herein relate generally to lignin, lignosulfonate, tannin, and tannic acid gels. In some embodiments, the gels are formed by reacting a low- or non-toxic crosslinking agent with lignin, lignosulfonate, or other gelling agents.
2. Background
Lost circulation is a recurring drilling problem, characterized by loss of drilling mud into downhole formations that are fractured, highly permeable, porous, cavernous, or vugular. These earth formations can include shale, sands, gravel shell beds, reef deposits, limestone, dolomite, and chalk, among others. Other problems encountered while drilling and producing oil and gas include stuck pipe, hole collapse, loss of well control, and loss of or decreased production. In attempting to cure these and other problems, crosslinkable or absorbing polymers, loss control material (LCM) pills, and cement squeezes have been employed, each of which may include materials such as lignins and lignosulfonates, as well as lignin and lignosulfonate gels.
Lignin is a by-product of the sulfite process of making paper, and when combined with sodium dichromate, forms an insoluble gel after a short time. Lignin-based grouts or gels can be used in porous earth formations for decreasing the flow of water through the formation, or for increasing the load-bearing capacity of the formation. Lignin grouts have also been used effectively in sealing fine fissures in fractured rock or concrete.
In addition to sodium bichromate, other crosslinking agents used in forming lignin-based gels include potassium bichromate, ferric chloride, sulfuric acid, aluminum sulfate (alum), aluminum chloride, ammonium persulfate, and copper sulfate. The bichromates have been the most widely used and are the most satisfactory, as they return a gel having a desired strength.
Lignosulfonate gels have also been used in gel treatments, such as to reduce channeling of solvent and water through drilling formations. In particular, chrome-lignosulfonate time-set gels have been found to be successful in forming an in-situ time-set gel. For example, see Wagner et al., “Field application of lignosulfonate gels to reduce channeling, South Swan Hills Miscible Unit, Alberta, Canada,” SPE 15547, 1986.
U.S. Pat. Nos. 3,672,817 and 4,001,205 disclose processes for producing a dispersant by reacting a water-soluble sulfonated lignin and epichlorohydrin. U.S. Pat. No. 4,168,371 discloses a process for making lignin-based gels by reacting a water-insoluble lignin and epichlorohydrin, where the reaction is catalyzed by an alkali metal hydroxide. U.S. Pat. No. 4,244,728 discloses a process for producing a crosslinked lignin gel which is the reaction product of an aqueous solution of alkali lignin with a crosslinking agent such as formaldehyde, glyoxal, or glutaric dialdehyde.
Lignin and lignosulfonate gels formed with bichromates, epichlorohydrin, and aldehydes, however, are no longer environmentally acceptable due to the toxicity of the chromium, aldehyde, and epichlorohydrin crosslinking agents. Unfortunately, other reactants may not result in a gel of equivalent strength as when these crosslinking agents are used. For example, lignin gels formed from ammonium persulfate generally have a strength approximately 40 percent of that of a similar grout mixture in which bichromate is used as a reactant.
Accordingly, there exists a need for lignin-based and lignosulfonate-based gels formed from less toxic or non-toxic crosslinking agents, and for gels that have equivalent or greater strength than those formed from epichlorohydrins, bichromates or other chromium catalysts, and other toxic crosslinking agents.